Lockout and recycling device for an apparatus for determining the listening habits of wave signal receiver users



Nov. 24, 1953 s. A. SCHERBATSKOY ET AL 2,660,511 LOCK OUT AND RECYCLING DEVICE FOR AN APPARATUS FOR DETERMINING THE LISTENING HABITS OF WAVE SIGNALRECEIVER USERS Filed Oct. 24, 1947 6 Sheets-Sheet 1 Central Station filament Trans.

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i Li l- Inventors Serge A Scherbotskoy By Robert L. Freeman i neli N 4, 1953 s. A. SCHERBATSKOY ET AL 2,660,511

LOCK OUT AND RECYCLING DEVICE FOR AN APPARATUS FOR DETERMINING THE LISTENING HABITS OF WAVE SIGNAL RECEIVER USERS Filed Oct. 24, 1947 6 Sheets-Sheet 3 Inventors Serge A. Scherbofskoy By Robert L. Freem n %ww9 W 1953 s. A. SCHERBATSKOY ET AL 60,511

LOCK OUT AND RECYCLING DEVICE FOR AN APPARATUS FOR DETERMINING THE. LISTENING HABITS OF wAvE SIGNAL. RECEIVER USERS 6 Sheets-Sheet 4 Filed 001:. 24, 1947 m zoCEw 2525 owl;

lnvenfol s Serge A. Scherbotskoy Robert L.Freem0n 72/40) L3 24, 1953 s. A. SCHERBATSKOY ET AL 2,660,511

LOCK OUT AND RECYCLING DEVICE FOR AN APPARATUS FOR DETERMINING THE LISTENING HABITS OF WAVE SIGNALRECEIVER USERS INVENTOR. Serge A. Scherbotskoy BY Robert L. Freeman S. A. SCHERBATSKOY ET AL Nov. 24, 1953 266051 1 LOCK OUT AND RECYCLING DEVICE FOR AN APPARATUS FOR DETERMINING THE LISTENING HABITS OF WAVE SIGNAL RECEIVER USERS 6 Sheets-Sheet 6 Filed Oct. 24, 1947 .9 29.2.5 amkzwo Q I}: I+JM Ll 5+ 52 .3 3m 2: 5 0 0% b 0 F $8 N bow Hwwow m+ mm 5N N b 8m 2m 58 o 1% INVENTORS Serge AScherboiskoy y Robert L. Fremon &0x/ 3 Patented Nov. 24, 1953 UNITED STATES PATENT OFFICE LOCKOUT AND RECYCLING DEVICE FOR AN APPARATUS FOR DETERMINING THE LISTENING HABITS OF WAVE SIGNAL RECEIVER USERS of Illinois Application October 24, 1947, Serial No. 781,990

30 Claims. 1

The present invention relates to apparatus for determining the listening habits of users of wave signal receivers. More particularly the present invention is concerned with a lock-out and recycling device for use with such apparatus and particularly for use with apparatus of the type employing a search signal generator. Specifically the present invention is an improvement on the arrangements disclosed and claimed in copending Scherbatskoy application, Serial Nos. 781,988 and 781,989, and co-pending Richards application, Serial No. 781,786 filed concurrently, herewith, and all assigned to the same assignee as the present application.

In the above mentioned co-pending applications there are disclosed and claimed various arrangements of the so-called search signal type of apparatus for obtaining with instrumented methods a continuous record of the transmitting stations to which a wave signal receiver is tuned, from which it is readily possible to analyze the listening habits of the users of such wave signal receiver. In such instrumented methods of determining the listening habits of wave signal receiver users the receivers in a large number of homes are metered or monitored to afford the basic information. From this information a statistical analysis of the various factors affecting the sales effectiveness of particular radio programs may accordingly be arrived at. In such a system employing instrumented methods it is contemplated that the selection of the system collaborator homes-that is the homes in which wave signal receiver use is to be loggedshall be on the basis such that all of the various factors, as for example the number of potential listeners, economic affluence, religion, etc. which normally afiect any process of sampling public opinion are accounted for on a weighted basis.

In the search signal type of device described and claimed in the abovementioned co-pending applications a search signal generator is employed which, in a more specific arrangement, cyclically, as for example, once per minute, scans the frequency spectrum by sending out a search signal which continuously or discontinuously varies in frequency during the cycle. This search signal has such a frequency composition that when the search signal frequency bears a predetermined relationship to that of the pass band to which the wave signal receiverbeing logged is tuned a response is produced in the wave signal receiver. In at least one embodiment of the search signal type of device, a single frequency component or monochromatic signal such as the output of a 5 or 6 kc. oscillator is superimposed on the search signal. The response produced in the wave signal receiver which might be referred to as a search tone is a signal having a frequency corresponding to the output of the 5 or 6 kc. oscillator. This response must be capable of being measured and this is accomplished by transmitting it to a recorder unit where a record of the response is made, the position of the response during the scanning cycle of the search signal generator being indicative of the particular frequency channel or pass band to which the wave signal receiver is tuned. By employing a monochromatic signal it is possible to make the response so weak as to be substantially inaudible, and yet with sufficient filtering and amplification it is capable of being measured without difficulty.

Since the strength of the search tone is greatly aliected by the conditioning of a receiver automatic volume control system for transmitter signals of various strength, there will be times when there is produced an audible heterodyne note or even search tone during the scanning cycle as the frequency of the search signal approaches and passes beyond the frequency of the carrier to which the wave signal receiver is tuned. In the above-mentioned co-pending Scherbatslzoy applications there are disclosed and claimed various means for producing a search signal which is substantially incapable of producing a heterodyne note due to intermodulation of the station carrier and the search signal. One such search signal included a random phase modulation component.

Even when the response produced by the search signal in the wave signal receiver being monitored is relatively inaudible and the heterodyne note is substantially inaudible the constant reoccurrence therecfcnce per minute may still be disturbing. Also it may cause substantial interference, in neighboring radios, particularly if the receiver being monitored is in an apartment building or other more congested residential area. It would be desirable therefore to provide a search signal type of device in which as soon as the tuning of the wave signal receiver being monitored is determined the periodic production of the search signal, at least on the channel tuned in by the receiver, is discontinued until the tuning of the wave signal receiver is changed.

Accordingly, it is an object of the present invention to provide an arrangement whereby lock out of the search signal generator with reference to one or more or all frequency channels occurs within a very short period after the wave signal receiver being monitored is tuned to a transmitting station.

It is another object of the present invention to provide a, search signal type of; device. in which the receiver response is produced in the receiver being monitored only when the tuning of the wave signal receiver is changed.

It is another object of the present invention to provide a search signaltype o f d'eyice with means for discontinuing the operation of; the, search signal generator fter the wave signal receiver has been tuned to a particular station, and to initiate the operation of the search sgnal' generator whenever the tuning of thewave s -gna l receiver is changed.

Still another object of the present invention is to provide an apparatus for determining the tuning condition of a wave signal receiver. of the type in which the bulk of the apparatus is z mct r m. h rece r lr ein mentored. and. u c n ec ed. e et xce throug a mmon ma pl an w c th p aratu emi e l z d. u le s th WW si n l. receiver is turned on.

t is u further ob c th resen vention to provide a lock-out arrangement for asea rch signal type of device for monitoring the tuning condition or a wave signal receiver in which lock-out of the search signal generator occurs on only a few channels such as, one for enample, and recycling of the searchsignal generator occurs in dependence upon the occurrence or a response in a different channel.

is a further object of the present invention to provide means for insuring recycling of the search signal generator whenever inadvertent loch-out thereof occurs.

Further. objects and advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed outwith particularity in the claims an" nexed to and forming a part of this specification.

For a better understanding of the present invention reference may be had to theaccompanym dr win s n which Fig, 1 is a bloc}; diagram of: a search signal type of apparatus embodying the present invention for monitoring a wave signal receiver;

liigs. 2a, 2b, and 2c are diagrammatic illustrations showing first, s econdand third portions of the system of Fig. l arranged so as to be united into a single disclosure for illustrating the details of the system of Fig. 1, Fig. 2a showing the details of the wave signal receiver and receiver attachment, and Figs. 2b and 20 showing the details, of the central station;

Fig. 3 is a schematic diagram of a detail of the arrangement shown in Fig} 2b; and

Figs. 4a. and 4b are diagrammatic illustrations showing first and second portions of a modincation of the present invention arranged so as to be united-into a single disclosure.

It will be understand that the lock-out and recycling devices of the present invention are applicable 'to various types of apparatus forindicating the tuning condition of wave signal receivers. For the purpose of a complete disclosure the invention is illustrated as applied to the specific apparatus disclosed in co-pending Scherbatskoy application, Serial No. 781,989 referred to above. As illustrated there is provided a search signal type of device for metering or monitoring a wave signal receiver to produce a record with respect to time of the tuning condition of such receiver. The search signal generator comprises means for producing a signal varying in frequency in a series of successively occurring steps, each. step. comprising a discrete frequency falling within various bands to which the receiver is likely to be tuned. The search signal generator operates. to produoethe. signal of step wise varying frequencies cl nfingv a scanning cycle preferably having a periodof one minute. The spectral da ag ng; the; cyclically produced search signal includes a modulation component preferablylin the form 03a monochromatic frequency cap or producing a response in the wave sig-- nal receiver in the. form of a search tone. The instant during the search cycle that a search tone or response .isproduced in the wave signal receiver being monitored is indicative of the particular frequency step of the search signal then being produced and consequently indicative of the par-- ticular transmitting station to which said wavesignal receiver; is tuned. A continuous record of this response with respect to the beginning of the search cycleprovides a continuous record ofthe stations to which. the wave signal receiver is tuned. The present invention is particularly concerned with arrangements for eliminatingany undesirable efiect from the audibility standpoint. ot-the-searchtoneor response.

Referring nowtzJ-Eig. 1 of thedrawings-there. is-illustrated awave signal-receiver. [0 to be monitored by the apparatusof the present invention. Ehis wavesignal receivermay beany type of wave signal receiver and neednot bethewell-known super-heterodyne type of receiver. which is. the. only type that can be. monitored by some prior art devices. The wavesignal receiver. l fl'.is.illustratecl; ascomprising an. antenna, ground circuit H and; a signal: reproducer or loud speakerl2 Associated with thewave signal receiver lflisa por-.. tion ofztheapparatus which. might bereferredto as the receiver. attachment I3. This receiverat-. tachment is. of. relativelysmall bulk whichis. gen-. erally capable. of being. disposedzwithin theayail.

- ablespace in evenvery. small receiver. cabinets.

The receiver attachment l3 and. the receiver [0 are connectedito a power. supply suchasthe house wiring circuit Mina-manner understoodby those skilled in. the art. Thehouse wiring circuit IQ provides a. sourceof power for the receiver.- and also. provides a channel. whereby the receiver, re.- sponse. which. is. converted; into. a. transmittable signalibythereceiver attachment [3 can be.transmitted't'o thecentral stationgenerally. designated at 5. preferably located in any suitable. place suchasithe basement. or acloset of the home in which the wavesignalreeeiver [B is located. The central. station. i5 includes, the precision ap-v paratus whichmay have. substantial bulk for re, cording the stationresponseand also includes .the searchsignal:v generator. to. be. described. herein.- after. A suitable. transmitting antenna. [6; is shown. associated. with the central station 15 whereby the. search. signal is. transmitted so as tobe picked up by the.- antenna. ground circuit H ofathe wavasignalreceiver Ill. Thehousewiring. circuit- Hi: islillustrated as. comprising, a. dotted line sectionto indicatetheremote relationship of thereceiver. Hl andt-he central-station I5.

For the purpose of picking out the search tone or response produced. in the. receiver ID by vir.- tue. of: the. receipt of" the. search signal. the. recei-ver attachment. I3! is illustrated: as connected to a circuitsuch. for exampleas the. audio circuit: of the wave. signal; receiver l0. preferably ahead of any tone or volume control in the receiver by means of a conductor l7. As is disclosed in one of the above mentioned Scherbatskoy co-pendingv applications however such a connection with the receiver It) is very simple and does not require disturbing the high frequency circuits in the receiver. Furthermore as is also disclosed in the above mentioned Scherbatskoy co-pending applications such a connection with the receiver may be completely dispensed with if desired. It will be apparent that such an arrangement little or no resistance will be encountered in placing such equipment in a collaborators home. The receiver attachment I3 is of such small bulk that in many cases it may comprise a volume no greater than that of an ordinary cigarette package and if no attachment whatever is made with the receiver the collaborater will have no fear that the operation of his receiver will be impaired. Furthermore the more bulky apparatus is located in an out-ofthe-way place in the home and no connections with this apparatus and the receiver are required other than connections of the individual apparatus to the house wiring circuit which is assumed to be present both where the receiver is located and where the central station is located.

Referring now to Fig. 2a of the drawings it will be noted that the details of the wave signal receiver l and the receiver attachment I3 are shown, although the particular construction of the wave signal receiver It] forms no part of the present invention. For the purpose of making a complete disclosure the wave signal receiver in is depicted as of the well-known superheterodyne type although it might equally comprise some other type of receiver. As illustrated the wave signal receiver it comprises a power supply unit 2c which is connected to the receiver attachment l3 through a plug connector 2i and a manually actuated switch 22. The primary winding 23 of the power supply transformer is shown connected in series with the manually operable switch 22. It should be understood that the switch 22 is preferably the standard form of switch employed on radio receivers which usually is combined with the volume control. In addition to the power supply unit the wave signal receiver It comprises a tunable radio frequency amplifier unit 25. an oscillator modulator unit 25, an intermediate frequency amplifier unit 26, a detector and automatic gain control unit 27, and an audio frequency amplifier. unit L28 connected in tandem in the order named. The antenna ground circuit ii is connected to the input of the tunable radio frequency amplifier 24, while the signal reproducer or loud speaker i2 is connected to the output of the audio frequency amplifier 28. The power supply unit 2i! is illustrated as being interconnected with the various stages of the wave signal receiver it for supplying the necessary plate voltage as well as filament current. The detector and automatic gain control unit 21 is illustrated as being interccnnected with several of the preceding stages by the automatic volume control circuit 29. As illustrated the detector and automatic gain control unit 2'? includes a detector tube 39 which has its plate circuit connected through a sui able tuned circuit Zita, a coupling capacitor 3i and a portion of a manually adjustable volume control resistor 32 to the control electrode or grid of an electron discharge valve '33 which may comprise the first audio stage of the wave signal receiver ill. The top of the automatic volume control resistor 32 is designated by the reference numeral'32w' It will be understood that this point 32a is readily available in most wave signal receivers such as IE3 without in any way disturbing the electrical circuits therein.

The operation of the wave signal receiver I!) described above will be apparent to those skilled in the art. Briefly radio frequency signals are selected and amplified by the tunable radio frequency amplifier 24. These selected signals are supplied to the oscillator modulator unit 25 where they are converted to a fixed intermediate frequency which is amplified in the intermedi-- ate frequency amplifier unit 26 and subsequently detected in the detector stage 21. These detected modulation signals of audio frequency are amplified by the audio frequency amplifier and reproduced in audible form by the signal reproducer i2.

Before considering the details of the receiver attachment designated as I 3 in Fig. 2a of the drawings whose purpose is to convert a suitable response or search tone in the wave signal receiver i i to a measurable signal which can be transmitted to the recording unit in the central station it, reference may first be had to Fig. 2b

of the drawings wherein is disclosed a portion of the apparatus of the central station I 5. Although any type of search signal generator may be employed there is illustrated the so-called center frequency search signal generator designated generally by the reference numeral 35. This search signal generator 35 is capable of producing during each scanning cycle a search signal the frequency of which varies in a series of discrete frequency steps, the frequency of each step being substantially equal to the transmitting frequency of an associated transmitter likely to be tuned in by the wave signal receiver Any suitable means for producing such a search signal may be employed. As illustrated the search signal generator 35 includes a section 35a comprising an oscillator controlled by a plurality of crystals which are capable of producing the rigorously controlled frequencies desired. Satisfactory crystals for producing frequencies in the frequency modulation band are not available and accordingly the section 351) of the search signal generator 35 is provided for producing during the search signal cycle a plurality of discrete frequencies in the frequency modulation band.

The section 35a of the search signal generator "is includesan electron discharge valve 3'! which is specifically illustrated as a pentode having an anode 38, a cathode 39, a control electrode 49, a suppressor grid 4! and a screen grid 42. For the purpose of producing a variable frequency search signal the frequency of which varies in a stepwise manner, the pentode 3? is operated as a crystal oscillator of the Pierce type with the discrete frequency steps accurately controlled by a plurality of crystals designated as 43a, 42b, 43c, tad, 43c and 63f which are arranged to be successively connected, once during earth scanning cycle, into the oscillator circuit including the electron discharge valve 31. As mentioned abc-ve each of the crystals 48a, 63b, 43c, 43d, ite, and ts is chosen to have a frequency which coincides with the frequency of a different one of the transmitting stations within the standard broadcast band likely to be tuned in by the wave signal receiver E0. It will be understood that for different localities diiferent crystals will be chosen. Preferably the crystal 43a has the lowest natural frequency somewhere within the range of 550 to 1600 kc. and the others are of progressively higher frequencies within the same range. Although only six such crystals are illustrated it should be understood that any desired number might be employed depending upon the number of transmitters to which the wave signal receiver I9 is likely to be tuned. The six crystals are illustrated by way of example only and the specific number chosen is unimportant as far as the present invention is concerned.

For the purpose of selectively connecting one crystal at a time into the oscillator circuit each crystal has one terminal thereof connected to the screen grid 42 of the elctron discharge valve 41. The other terminals of the crystals $311, 431), 43c, 63 13s and 43/ are each connected to a different one of a plurality of contacts ida. 44b, Mic, did, He and M1 repectively which are arranged together with a plurality of contacts Mg, Mb, 351' and My along with the periphery of a circle in equally spaced relationship so as to form with a rotating switch arm 45 a rotating switch mechanism. As will be brought out in greater detail hereinafter the rotating switch arm 45 is preferably adapted to be driven at a constant angular speed preferably at one revolution per minute so that the terminals or contacts 44a to 4137' are successively engaged at equally spacd time intervals. The terminals its, rich, and My have no function whatever and could omitted so long as the space and arrangement of the other terminals remains unchanged. It ought furthermore be understood that ii the section 351) of search signal generator were not employed that the terminals ita to car would preferably be arranged around the circumference of a circle at equally spaced intervals. Such an arrangement is shown in the above mentioned co-pending Richards application. However, the terminals t ig, MIL, and ie-ti correspond to intervals when search signals are produced the section 352) of the search signal generator 35 and at those times and also at the time correspond ing to the terminal M7 the section of the search signal generator 35 is inactive.

In order that the crystals led to 33] are connected to control accurately the stepwise varying frequency of the search signal the movable switch arm '45 is connected by means of a conductor to the control electrode 45- of electron discharge valve 3?. The cathode 39 of the pe-ntode 3'? is preferably grounded as indicated at 8 and a suitable feed back capacitor it and a grid leak resistor 50 are provided. The screen grid i2 is furthermore connected to a conductor through a voltage dropping resistor 52. The conductor 5! as will be described hereinafter is connected to a suitable source of +5 potential. Suitable radio frequency bypass capacitors and at are also provided. With this arrange ment it is apparent that the crystals oscillate in the mode of the Pierce circuit.

In order that the search signal, varying in frequency in a stepwise fashion, appearing in the plate circuit of the pentode 3? is supplied. to the transmitting antenna [6 so that it can transmitted to the wave signal receiver ii) for interception by the antenna ground circuit ii, the plate circuit of the electron discharge valve 37 is connected to a source of +3 potential such as the conductor 5| through a conductor 55, a plurality of parallel connected net works, and a rotatable antenna attenuator switch comprising the movable switch arm 56 and a plurality of contacts 51a, 51b, 51c, 51d, 51c, 51f, 51g, 51h, 512', and 517' arranged in equally spaced relationship along the periphery of a circle. As illustrated the contacts 51a to 52'? inclusive are positioned in exactly the same manner as the contacts 34a to Ma and the contacts marked with the corresponding letter are simultaneously engaged by the associated rotatable arms 55 and 5 respectively. Each of the parallel connected networks comprises a resister 58 specifically designated as 58a, 58b, 58c, 58d, 58c and 58] respectively for the different networks and a capacitor 55% specifically designated as 59a. 59b, 55c, SM, 598 and 59] respectively for the various networks. Each capacitor 59 is adapted to parallel a variable portion of its associated resistor 53. The resistors 58 are provided to insure that the direct current plate voltage remains constant at all times so as not to cause variations in the output frequency of the oscillator. However, for the purpose of produc ing the desired attenuation of the alternating current signals of discrete frequencies produced by virtue of the plurality of crystals 43a to lSf, the variable impedance paths through the capacitors 53 and the variable portions of the resistors 58 are provided. With this arrangement a uniform intensity of the search signal throughout the scanning cycle is obtained. The contacts 519, 57hand 512' of the antenna attenuator switch are connected to the plate circuits of the oscillators of the section 3527 of the search signal generator so that +B plate potential may be applied thereto through the rotatable switch arm 58, and the conductor 55 at dilferent predetermined instants during the search signal scanning cycle. The antenna it is coupled to the plate circuit of the pentode 3i by means of a suitable coupling capacitor 58.

In order to produce a search signal which comprises a plurality of discrete frequencies varying in a stepwise manner, each discrete frequency step occurring once during each search or scanning cycle and at exactly the same position during each cycle, there is provided a synchronous motor and gear train unit 6!, which is adapted to be connected with the house wiring circuit Hi through suitable control circuits to be described hereinafter, inciuding the conductors 62 and B3. Preferably the synchronous motor is adapted to rotate the switch arms 65 and 55 by means of an interconnecting shaft generally designated at El at one revolution per minute. The shaft 6% of the synchronous motor unit Si is also adapted to rotate a third switch arm G l which with the contacts a, (55b, 25c, 65d, 65c, 55/, 6551, 6571, 852', and 657' provides a stylus selecting switch with reference to a plurality of styli 6'? forming a part of a recorder unit 68. As illustrated the terminals or contacts 65a to 652' inclusive of the stylus selecting switch are adapted to be connected by suitable conductors extending in a cable 86 to the individual Styli Bid, 'fiib, 8'50, fiid, Sic, so, My, 61h, and Sit respectively of a recorder 68 to be decribed hereinafter in greater detail. The switch arms 45, 56 and 8 are all disposed in the same angular position with reference to shaft 6| so that the associated contacts marked with the same subscript are simultaneously contacted by all three switch arms 5, 58 and 66. Accordingly, the contacts or terminals 65a, 65b, 65c, 65d, 65c, 65}, 559, 857i, Gfii and 657' are also arranged along the periphery of a circle in exactly the same manher and order as the contacts or terminals M and 5?. The synchronous motor 8| is preferably of a type which is capable of starting and stopping substantially instantaneously, the reason for which will become apparent from the following description.

Although the wave signal receiver i has been illustrated as one for receiving the standard broadcast band, it will be understood that it might equally well a frequency modulation receiver or at least be provided with frequency modulation channel. In order that information with respect to the tuning of a wave signal receiver to stations transmitting frequency modulated signals may be recorded, the frequency spectrum of the frequency modulation band must also be scanned by the search signal generator 35. As was mentioned above crystals capable of producing oscillations in the frequency modulation band are not generally available. If they were the search signal generator 35 would merely be provided with additional crystals each having a natural frequency corresponding to the transmitt-ing frequencies of different frequency modulation stations to which the wave signal receiver being monitored is likely to be tuned. As was brought out above by having the search signal frequency during each scanning cycle composed of a plurality of discrete frequency steps, the frequency of each step being equal to the transmit ting frequencies of a plurality of different transmitting stations to which the wave signal receive-r might be tuned, no audible variable pitch heterodyne note can be produced, since to produce an audible variable pitch heterodyne note it is necessary to have two inter-modulated frequencies which produce a variable frequency beat fr quency in the audible range. Furthermore when the frequencies of the intermodulated signals are almost exactly equal the beat frequency is obviously inaudible. In view of the present invention as will become apparent from the following description absolute inaudibility is not a requirement.

As illustrated in the drawings the section 35b of the search signal generator 35 is capable of producing a search signal whose frequency varies in a stepwise fashion, in three discrete frequency steps during each cycle of the search signal which steps are a continuation of the discrete frequency steps produced by section 35a of the search signal generator 35. In other words the search signal generator 35 produces a search signal having nine discrete frequency steps, six of which are within the standard broadcast band produced by the section 355a and three of which are in the frequency modulation band produced by section 351).

As illustrated in Fig. 2b of the drawings, the section 351) of the search signal generator 35 includes three very high frequency oscillators hereinafter designated as V. H. F. oscillators To and specifically designated by the reference numerals 1g, lllh and Edi to correspond with the contacts My, 51h and 572' respectively, to which the plate circuits of the V. H. F. oscillators iii are respectively connected. The details of the V. H. F. osoillators l!) form no part of the present invention and are shown in block diagram in Fig. 2b of the drawings. However, for the purpose of a complete disclosure, one type of V. H. F. oscillator which was satisfactorily employed is illustrated in 3 of the drawings and is substantially identical with the V. H. F. oscillator described as a tuned circuit oscillator for the very high frequenoy range at page 372 and 373 of the 1946 edition of The Radio Amateurs Handbook.

The V. H. F. oscillator lei which is identical th the osc l ted 1971 and 19 s s arp in n- 'also through windings 83g, and 83h respectively con- 16. variable resistors in the form of electron dis- .and a control electrode or grid 8?. circuits of each valve are connected in parallel to produce a low internal tube resistance.

conventional fashion in Fig. 3 of the drawings to show how the tube elements are tied in with circuit construction. The corresponding parts are designated by the same reference numerals as in the preceding figure. Basically, the oscillator comprises two heavy brass plates Ho and Nb which act both as tube mounting supports and as the stator plates of the tuning condensers l2 and 113 respectively. For the purpose of reducing the circuit inductance an electron discharge valve of the 6F4 type which has symmetrically arranged grid and plate leads is employed, designated as T l in the drawings. This tube or valve 14 comprises an anode supported by the brass plate .Ha, a cathode 16, a control electrode or grid 7! supported by the plate Nb, and a filament 73. The inductance is furthermore kept low by shunting the lead wires to the tube 14 by the low inductance brass plates Ha and lib. A pair of small inductance coils 59a and 1917 which represent most of the inductance of the circuit are connected to the brass plate lia. By properly choosing these coils and properly adjusting the capacitors l2 and 13 the desired oscillator frequency may be obtained. Plate potential or +13 potential is supplied to a tap 83 on one of the inductances such as 1911 through a suitable voltage dropping resistor 8!] from an associated contact .such as 512 of the rotary switch including the switch arm 55. With this arrangement it is apparent that +3 potential from the conductor 5| is applied successively to the oscillators 73g, llih and mi in that order at the instants the asso ciated terminals 519, Em and 511' respectively are contacted by the rotating switch arm 55. The

ence numerals 8Ig, 81h and 8H respectively. In order to supply the oscillations to a transmitting antenna which may be the antenna [6, but preflerably is a separate antenna such as 82, one of the windings such as 1911 is inductively coupled to a winding 831' in the circuit of the antenna 82. The plate circuits of the oscillators 79g and lllh are inductively coupled to the. antenna 82 nected in series with the winding 832' as is clearly ,shown in Fig. 2b of the drawings.

For the purpose of controlling the oscillations of the V. H. F. oscillators in a variable resistance is connected in series with each of the cathodes As illustrated in Fig. 2b of the drawings charge valves 84g, 847:. and 3 32' respectively are connected in series with the cathodes '56 of each ing a pair of anodes 85, a grounded cathode 36 The plate The oscillator circuits are so adjusted that when zero or a positive voltage is applied to the control electrodes 8'! which are all connected in parallel -through suitable parallel arranged resistors 88, the oscillators will produce oscillations when supplied with plate potential.

From the detailed description included above it is apparent that the search signal generator 35 equal to that of various amplitude modulation and frequency transmitters which are likely to be tuned in by the wave signal receiver being metered or monitored.

For the purpose of producing a recordable index signal of the tuning condition of the wave signal receiver Iii the spectral composition of the search signal produced by the search signal generator 35 should be such that it is capable of producing a response in a frequency selective circuit such as the wave signal receiver I0. As was discussed in the above mentioned co-pending Scherbatskoy applications a very satisfactory search signal is one which includes a modulation component of a single component or monochroinatic frequency which can be filtered by a narrow band pass filter and which furthermore is of such a frequency as to be outside the range of maximum sensitivity of both the wave signal receiver I9 and the human ear. A satisfactory monochromatic signal has been found to exist in the frequency range of 5,000 to 6,000 cycles. A response of this frequency produced in the receiver If] is within the pass band of the receiver and such a response or search tone will be produced in the receiver whenever the frequency of the search signal produced by the search signal generator 35 is equal to the frequency of the station carrier tuned in by the wave signal re- I ceiver [0. Accordingly there is provided at the central station I5 a generator capable of generating a 5 kc. signalwhich is illustrated in Fig. 2b of the drawings as a 5 kc. oscillator 89 which is adapted to supply a modulation component to both sections 35a and 35b of the search signal generator 35.

It should be understood that the 5 kc. oscillator may comprise any standard form of oscillator capable of producing a monochromatic signal and the 5 kc. frequency is furthermore not essential since other frequencies might be employed such as 6 kc. for example. As illustrated oscillator 89 comprises an electron discharge valve, 90 having an anode 9|, a cathode 92, a control electrode 93 and a screen grid 94. A tank circuit 95 has one end thereof coupled to the control electrode 93 by means of a capacitor 96. This control electrode 93 is also connected to ground through a suitable grid leak resistor 91. For feed back purposes the cathode 92- is connected to a suitable tap 99- on the inductance of the tank circuit 95. The tank circuit 95' is also coupled to the plate circuit of the electron discharge valve 90 by means of a capacitor 99 and a resistor I00. The screen grid 94 is connected to a source of +B potential through a suitable conductor I III and a voltage dropping resistor I92. The plate 9| is also connected to the conductor IO I through the resistor I02v and a winding I03. The winding I03 forms a part of a coupling means I04 for coupling the output of the oscillator 89 to the control electrodes 81 of the variable resistor tubes' 85. Any other coupling means might be employed however. The 5 kc. output from the oscillator 89 therefore changes the conductivity of the tubes 85 and consequently the internal resistances thereof. When the internal resistance is decreased sufiiciently the resonant circuits of the oscillators Iii are damped sufiiciently to stop oscillations. Consequently the search signal produced by the section; 35b of the search signal generator 35 inaddition to varying in frequency in a stepwise manner is also pulsed or amplitude modulated at a frequency of 5 kc.

To cause the. search signal produced by the section 35a of the search signal generator 35- to include a 5 kc. modulation component capable of producing a response in the wave signal receiver I9, the plate circuit of the 5 kc. oscillator 891s also coupled to the suppressor grid GI of the pentode 31 through a suitable coupling capacitor Ill? and a resistor I08, which resistor I98 permits an initial adjustment to be made. The suppressor grid M is also grounded through a suitable resistor I09. Consequently the output of the search signal generator 35 comprises a search signal composed of a succession of discrete frequencies occurring in a stepwise fashion all amplitude modulated with a 5 kc. modulation component.

It will be understood that if no frequency-modulation channel is embodied in the wave signal receiver I that the section 551) of the search signal generator 35 may be omitted. It will be understood that any other type of search signal generator may also be employed so long as it is capable of producing during a scanning or search cycle a variable frequency signal either continuously or discontinuously variable as disclosed in the above mentioned copending application filed concurrently herewith.

It will be apparent that operation of the receiver attachment I3, the details of which are described hereinafter as well as operation of the central station I5 require a source of power both for the filaments of the tubes involved as well as for the plate potentials and the various bias potentials. It is furthermore desirable that such power be supplied only when it is desirable to monitor the receiver II] and record information relative to the station or stations to which a receiver is tuned or in other words only when the receiver I0 is turned on. Obviously then the power supply for the receiver attachment i3 and the. central station l5, should not be rendered effective to supply the necessary electrical energy unless the receiver Ill is turned on.

The power supply unit for the receiver attachment is specifically designated in Fig. 2a of the drawings by the reference numeral IIII. Preferably the power supply unit I II] is connected through the contacts I I la of a relay II I and the plug connector 2 la to the house wiring circuit I4. The winding of the relay III is connected in series with the receiver power supply through the manually actuable switch 22 of the receiver I9 and the plug contact 2|. Whenever the receiver I9 is turned on through closing of the switch 22 current flows to the receiver power supply unit 20 which is of sufficient magnitude to pick up relay I I I and close the contacts I I la with the result that the power supply unit lid is energized. This power supply unit includes an auto-transformer H2 to which is coupled a winding H3 for supplying the filaments of the electron discharge valves employed in the receiver attachment I3. The portion II2a of the auto-transformer H2 is connected through the contacts IIIa across the house wiring circuit I4 through the connector or plug contact 2Ia. The complete transformer winding on the other hand is connected in series with the rectifiers H4 and H5 and a suitable resistor I I6 with the plate circuits of the electron discharge valves in the receiver attachment I3 so as to supply the necessary +13 potential. A suitable filter capacitor ii! is connected across the output terminals of the +B source of potential for smoothing purposes. The other terminal of the power source H6 is grounded as indicated at IIB.

As has been mentioned in connection with Fig.

a conductor I3 I.

a part of a remote control unit I39.

relay I31.

anode I4I.

its contacts ace -511 1 of the drawings the only electrical circuit interconnecting the central station I and the wave signal receiver I0 is the house wiring circuit I4. This is also true of the receiver attachment I3 and the central station I5. It will be understood that the house wiring circuit !4 could be employed as a remote control circuit for energizing a power supply unit designated at I and located 'at the central station I5 in response to turning on switch 22 is closed. As illustrated the oscillator I2I is designated as a 9 kc. oscillator. Any conventional type or oscillator may be employed for this purpose and as shown in the drawings this oscillator comprises an electron discharge valve I22 having a cathode I23, an anode E24 and a control electrode :25. The tank circuit for the oscillator comprises an inductance I25 and a capacitance I21. The tank circuit is magnetically coupled as by the winding I28 and the coupling capacitor I29 with the control electrode or rid I 25 and the oscillator tube i 22.

The control electrode I22 is connected to the cathode I23 through a grid leak resistor l3ii grounded as indicated. A source of plate potential from the output of the power supply unit II is connected to the anode I24 through the inductance E25 and The plate or output circuit of the 9 kc. oscillator I2I is connected through a conductor I 32 to the ungrounded side of the house Wiring circuit I4 whereby the 9 kc. oscillations ii above the audible range of both the signal reproducer I2 and the human ear.

The power supply unit I20 at the central station l5 comprises a power supply transformer I35, the primary winding I a of which is connected across the house wiring circuit I 4 through a suitable plug connector generally indicated at I34 and the contacts I3'Ic of a relay i3? forming The remote control unit I35 includes means for closing the normally open contacts I3'Ia of the relay I31 in response to the closing of the wave signal receiver switch 22 which causes a 9 kc. signal as described above to be supplied to the remote control unit I30. As illustrated the remote control unit I 35 includes a gas triode I 30 the plate circuit of which is connected in series with the winding of the This gas triode I38 includes an anode I39, an ionic cathode I and a grid or starter Such a gas triode I33 may be of the type designated as 0A4. In such a gas triode a relatively small amount of the electrical energy supplied to the starter anode 145 initiates a glow discharge between the cathode I40 and the starter anode I4I so as to start the main discharge between the plate I39 and the cathode I40 with the resultant energization of the relay I3! to close 3141. As illustrated the starter anode I41 is connected between two bleeder resistors I42 and I43 arranged in series across the ,tential source. I50 is connected through a suitable smoothing tubes I59 and IE0. .tential appearing at the plate of the voltage regulator I59 is connected by means of a conductor .tential. ode connected to one terminal of the secondary winding 351; of the transformer I35.

14 nected across the power line or house wiring circuit I4 in parallel with the bleeder resistors I42 and I43. The terminal of the capacitor I con nected to the inductance I44 is connected to the cathode I40. This tuned circuit is made resonant at 9 kc., so that when the 9 kc. oscillations produced by the 9 kc. oscillator I 2! are received at the remote control unit I36 a resonant voltage appears across each component of the tuned circuit comprising the inductance I44 and the capacitor I45. The efiect of this voltage across the capacitor I45 is to increase the negative potential peaks on the cathode I40 and thus eifectively to increase the potentials between the cathode I4 and the starter anode I4I. Consequently these voltage peaks start a discharge between the cathode I40 and starter anode MI so as to start the main discharge between the anode I39 and the cathode I40. Because alternating current is supplied to the anode 39 the gas triode I38 ceases to discharge when the 9 kc. oscillations are removed. Consequently the remote control unit I36 is capable of energizing and deenergizing "the primary winding I350. of the power supply transformer I35 in response to the closing of the receiver switch 22 without any connection between the two circuits except the conventional power line.

The power supply unit I20 also includes a rectifier I whose anodes I5I and I52 are connected to the end terminals of the secondary winding I352) of the transformer I35 in the manher of a full-wave rectifier. The filament curof the power transformer I 35. The center terminal I53 of the transformer secondary winding i35b is grounded as indicated at I54 and provides the negative or ground terminal of the B po- The cathode I55 of the rectifier filter I56 to the terminal I51 which is the +3 terminal of the plate or 13 potential source. For

.the purpose of providing a regulated plate p0.- Vtential a series circuit comprising an adjustable resistor I58 and a pair of voltage regulator tubes I59 and I60 are connected across the terminals I54 and I51.

Also a capacitor Hit is connected across the series connected voltage regulator The highly regulated +B po- I52 to control circuits described hereinafter. Another regulated source of +B potential appearing at the plate of the voltage regulator tube I60 is supplied to the conductor IilI which is connected and the resistor l 58 is in effect a current limiting resistor connected in series with the gaseous voltage regulator tubes for producing satisfactory operation thereof.

The power supply unit I20 also supplies to a voltage divider unit I a suitable biasing po- As illustrated a diode !34 has its cath- The plate of the diode I64 is connected, through an ad- .justab'le resistance H55 and a smoothing and voltage regulating unit I58 to the ground terminal I54. A negative biasing potential appear- 15 It should be noted that the conductor 52 from the synchronous motor (BI is connected to the grounded side of the house wiring circuit as indicated at I69. This side of the house wiring circuit is preferably grounded through a suitable capacitor I10, as far as the high frequencies transmitted thereover are concerned without however grounding the line as far as the ISO-cycle power is concerned.

For the purpose of picking up a signal in dicative of the response produced in the wave signal receiver II] by the search signal created by the search signal generator 135 there is provided in the receiver attachment I3 a tuned amplifier unit generally designated at I15 which tuned amplifier unit is equivalent to a band pass filter and an amplifier. The details of the tuned amplifier unit I15 are unimportant as far as. the present invention is concerned. This tuned amplifier is sharply tuned to a frequency of. 5 kc., which is the frequency of the search tone produced in the receiver If! as described above. To limit the frequencies picked up by the tuned amplifier I to a very narrow frequency band it is provided with three cascaded tuned circuits comprising the tuned circuits I15, I11 and I18. The tuned amplifier I15 further includes a plurality of electron discharge valves I19, I20, and IBI for amplifying the 5 kc. signal supplied to the tuned amplifier I15. The plate circuits of these electron discharge valves are connected to the conductor I3I mentioned above which is connected to the source of plate potential at the power supply unit III].

In order that the response produced in the wave signal receiver I0 may be received by the tuned amplifier I15 the input thereof may be coupled through a coupling capacitor I 92 to a microphone or the like positioned adjacent the signal reproducer I2 of the wave signal receiver ID, or as illustrated, may be connected to the terminal 32a at the top of the volume control of the wave signal receiver I9. Preferably the capacitor I82 is very small. Such a connection can readily be made without disturbing the high frequency circuits or even the audio circuits of the receiver ID. The alternative arrangement suggested above employing a microphone is shown in the co-pending Scherbatskoy application Serial No. 781,988 referred to above and no connection. whatever with the receiver is required in such case.

As illus ated in the drawings the output of the tuned amplifier I15 is connected by means of a coupling capacitor I83, which resonates with. inductance to form one tuned circuit of the tuned circuit I18 and the conductor I32 with the house wiring circuit I4 so that the response in the form of a 5 kc. signal may be supplied to the central station I5 to be recorded by the recorder 68.

In order that a record of the search tone produced in the receiver I!) may be made by the recorder 68, the central station I5 is provided with a 5 kc. control channel comprising a 5 kc. band pass filter I84 and a 5 kc. amplifier and relay unit I85. The 5 kc. band pass filter I84 is connected through a coupling capacitor 186 and. a conductor I81 to the ungrounded side of the house wiring circuit I I through the con tacts I311: of the relay I31. The capacitor I 85 prevents oil-cycle current from entering the 5 kc. channel while still providing a path for the 5 kc. current. The 5 kc. filter I84 is a very sensitive filter illustrated as a Z-mesh filter. It is apparent therefore that very high selectivity of the 5 kc. search tone frequency is obtained since the tuned amplifier I15 in the receiver attachment is provided with three tuned circuits, each circuit tuned to 5 kc., and the band pass filter I84, is provided with a two-mesh tuned cirsuit. The band pass filter I84 also includes a built in attenuator comprising the resistor I88.

In order that the single frequency component or monochromatic signal passed by the band pass filter I84 may be caused to produce a record of the response in the recorder unit 68, to be described hereinafter, the output of the band pass filter I 84 is preferably supplied. in succession to a 5 kc. amplifier I 89a, a rectifier IBM, and a direct current amplifier I9Ia which is adapted to control the energization of a stylus control relay I93 all forming a part of the 5 kc. amplifier and relay unit I85. As illustrated the 5 kc. amplifier I89a comprises a section of a twin triode I89 while the rectiier IQIJa comprises a section of the twin diode I99. Also the direct current amplifier I9Ia comprises a section of the twin triode I9I. The other sections of the twin tubes I89, I 95 and HM will be described in connection with the functions which they perform described hereinafter. It will be understood that separate tubes may be employed rather than the twin tubes illustrated. The con trol electrode of the 5 kc. amplifier IBM is con nected to a suitable voltage divider disposed at the output of the band pass filter I84. The plate circuit of the amplifier IIIQa is coupled to the rectifier I9Ila through a suitable coupling capacitor I54. The cathode of the rectifier [90a is connected through a resistor I with the control electrode of the direct current amplifier I9Ia. In order to prevent operation of the 5 ho. amplifier and relay unit I85 unless a 5 kc. signal representative of the search tone or response in the receiver III is applied thereto negative bias potential from the voltage divider unit IE3 is supplied to the control electrode of the direct current amplifier IS! a through a resistor I91. A suitable capacitor I99 connected across the resistor I91 cooperates with. the resistor I95 so as to provide a circuit with a long time constant to prevent any signal such as static or an occasional click from causing inadvertent operation of the 5 kc. amplifier and relay unit I85. This arrangement insures operation of the stylus control relay I93 only in response to the existence of a true search tone produced by virtue of the operation of the search signal generator 35.

Plate potential is supplied to the amplifier I89a from the conductor I62 which is a source of +3 potential through a coupling resistor 266. The plate circuit of the direct current amplifier I9Ia is also connected to the conductor I62 which is a source of -[B potential through the normally closed contacts 202a, the winding I93 of the relay I93 and the milliammeter 204. The contacts 2920: of a relay 202 are illustrated as forming a part of an additional control device to be described hereinafter, but it should be understood that the search signal type device described thus far will function without this relay. If this relay is omitted suitable means for bridging the circuit at the contacts 292a would be provided. The magnitude of the bias potential applied from the unit I53 to the control electrode of the D.-C. amplifier I9Ia is adjusted so that a low current of for example one milliampere flows through the P milliammeter 2M and the Winding I93 of the associated relay I93 when no kc. signal is received by the 5 kc. amplifier and relay unit I85 which is insufficient to cause operation of the relay I93. When a response or search tone is produced in the wave signal receiver Ill, however, a 5 kc. signal is transmitted through the 5 kc. channel in the central station I5 which is rectified by the rectifier Iiifla and supplied to the control electrode of the direct current amplifier ISIa to cause a substantially larger current as for example a current of milliamperes to flow through the wind ing I93 of the stylus control relay I93 whereupon this relay is energized to close its normally open contacts I93a.

It will be apparent from the above description that the amplifier I89a, the rectifier I 90a, the direct current amplifier I 9Ia and the relay I93 comprise a 5 kc. relay unit I35 which performs a control function whenever a signal responsive to the search tone produced in the wave signal receiver is applied to the control electrode of the amplifier IBQa. This unit I85 is adapted to control the operation of the styli 61 of the recorder 68. As illustrated the closing of the contacts I93a supplies +B potential from the conductor I62 to the switch arm 64 of the stylus control switch through a voltage dropping resistor 206 and the conductor 201.

In describing the search signal generator 35 and the synchronous motor 6! no complete description was included as to the circuits for supplying alternating current to the synchronous motor BI and +B potential to the search signal generator 35. As illustrated in the drawings, the synchronous motor 6| is connected to the house wiring circuit I4 through conductor 62 which leads directly to one side of the house wiring circuit and the conductor 63 which is connected to the other side of the house wiring circuit through the pole 268a of a 3-pole manually actuable control switch 208, the conductor 208, the conductor I81 and the contacts I31a of the relay I31 of the remote control unit I 36. As long as the pole 208a of the manual switch 208 is in the solid line position indicated in the drawings the synchronous motor BI is continuously energized whenever the switch 22 of the wave signal receiver I0 is closed. Such operation of the search signal generator is generally referred to as continuous scanning operation and the solid line position of the B-pole switch 288 may be referred to as the continuous scanning position. A suitable capacitor 2m is indicated as arranged in parallel with the switch pole 268a to eliminate arcing when the circuit to the synchronous motor 6| is interrupted. The manually actuable control switch 208 also includes a switch pole 208i) and a switch pole 2080. In the continuous scanning position of the switch 288 the pole 2680 performs no function. However, the pole 208D completes the circuit from the source of +3 potential such as from the conductor I82 through the contacts 262a and the switch pole 2881) to the search signal generator 35 and specifically to the conductors 55 and SI through the conductor 2! i, the conductor 2 I2 and the voltage dropping resistor 2I3. The pole also supplies +B potential through the conductor 2H and a voltage dropping resistor 2M to a stylus 61 of the recorder 68 to be described hereinafter.

For the purpose of producing an appropriate record indicative of the tuning condition of the receiver II] there is provided the recorder 68 referred to above and indicated as comprising ten styli 61a to 617' inclusive. It will be understood 18 that the type of recorder employed is immaterial as far as the present invention is concerned and the particular recorder shown in the drawings is chosen by way of example only. As illustrated the recorder 68 includes a movable recording element 215, continuous movement of which in the direction of the arrow is caused by rotation of a sprocket 2 I 6. The recording element is specifically illustrated as a tape having perforations along the edges for engagement with the teeth on the sprocket 2 I6. Preferably the sprocket 2I6 is driven by a synchronous motor 2" connected to a suitable source of power 2I8 so as to be driven continuously regardless of whether the other elements in the central station I5 are energized or not. Consequently the synchronous motor 2I1 should not be energized from the power supply unit I26 unless it is connected to the circuit ahead of the contacts I31a of the relay I31. The recorder 68 further inliudes a suitable take up spool 2 I9 and a tape supply spool not shown. As illustrated the recording element or tape 2I5 is a chemically responsive element such for example as an electrolytic paper. When an electric current is passed through such an element a chemical action occurs which produces a trace thereon at the point of current flow. To this end the recording element or tape 2I5 passes over a conducting shoe 220 which is grounded as indicated at 22I. It will be apparent therefore that whenever a potential such as a +3 potential is supplied to any one of the styli 61a to 617' a current flows through the tape 2E5 and the resultant chemical action causes a trace to be produced on the recording element 2I5 beneath the contacting portion of the particular stylus 61 which is energized, since this contacting portion is directly over the grounded conducting shoe 220. Due to the positioning of the styli 61 transversely of the tape 2I5 the transverse position on the tape of the trace produced by the styli is indicative of the station to which the wave signal receiver I0 is tuned.

In view of the fact that the styli 61a to 61i are connected to various terminals of the stylus selecting switch comprising the rotatable arm 64, it will be apparent that a trace will be produced on the recording element 2 I5 by whichever stylus,

is energized, when a search tone occurs in the receiver I0 during the scanning cycle of the search signal generator with the resultant energization of the stylus control relay I93 to close its contacts I93a. It will furthermore be apparent that each of the styli 61a to 612' corresponds to a particular frequency step in the search signal whose frequency varies in a step wise fashion during each cycle of the search signal generator and consequently corresponds to a particular pass band to which the wave signal receiver I0 may be tuned. If, for example, the wave signal receiver I0 is tune-d to a transmitter having a frequency equal'to that of the crystal 43a of the search signal generator 35, then it will be apparent that a search tone will occur in the wave signal receiver Ii! whenever the rotatable switch arm 45 engages its contact 44a. This search tone will cause the stylus control relay I93 to close its contacts IBM in a manner described above at the instant the arm 45 engages its contact 440:. At this instant during the search cycle the arm 64 of the stylus selecting switch engages its contact a whereupon the stylus 61a is energized to produce a trace on the recording element 2I5. When the rotating switch arms 45, 58 and 64 leave their associated contacts marked with the subscript a and the wave signal receiver I continues to be tuned to the transmitting station having a transmitting frequency corresponding to that of the crystal 43a the search tone in the receiver is discontinued with the resultant deenergization of the relay I93. Furthermore the stylus selector switch having the rotatable arm 64 causes deenergization of the stylus 61a. During the succeeding cycles of the search signal generator 35 the stylus 61a is again energized and this continues as long as the wave signal receiver I0 remains tuned to the transmitting station having a transmitting frequency equal to the frequency of the crystal 43a. Consequently a trace in the form of a dashed line will be produced by the stylus B'Ia on the element 255 as long as the synchronous motor BI is continuously energized and the tuning of the wave signal receiver I0 is unchanged. It will furthermore be apparent that if the wave signal receiver I0 is tuned to any other station corresponding to a frequency step in the cycle of the search signal generator 35 that a corresponding stylus 61 of the recorder 68 will be energized to produce a trace in the form of a dotted or dashed line on the recording element 2 I5.

As a practical matter there is a limit to the number of styli 61 likely to be provided in the recorder 68. Generally the number of styli provided would correspond to the stations which are likely to be tuned in often by the wave signal receiver I0. Occasionally however, the wave signal receiver II] will be tuned to stations other than those for which a stylus '57 is provided. Information relative to the tuning of the wave signal receiver It to stations other than those for which styli 61a to 612 are provided, is often very valuable to the analysis organization obtaining information relative to the listening habits of wave signal receiver users. Accordingly the recording stylus 617' is provided in the recorder 68 which may be referred to as the all other stations stylus. As is apparent from the above description the all other stations stylus 617' is energized whenever the wave signal receiver i0 is turned on through operation of the switch 22. Consequently when only a trace by the stylus .617 appears on the recording element 2 I5 it indicates that the wave signal receiver I8 is tuned to what may be referred to as all other stations, namely those stations for which no specific stylus 61 is provided in the recorder 68. Only when in addition to the trace produced by the stylus 617' some other trace by some other stylus is also produced is the wave signal receiver I0 tuned to a transmitting station specifically provided for in the search signal generator 35. It will be apparent that if only the trace produced by the stylus 61 appears on the recording element 2I5 for substantial periods of time that an indication is provided that the search signal generator should be provided with means to produce additional or other steps in the search signal whose frequency varies in a stepwise manner.

In view of the detailed description included above the operation of the center frequency search signal type of device when set for continuous scanning operation will be apparent to those skilled in the art. As long as the wave signal receiver Ill is turned off the central station I5 is deenergized except for the recording element motor ZIE which is preferably continuously energized. Upon actuation of the receiver switch 22 the central station I5 is energized through operation of the remote control unit I36 which causes power to be supplied to the driving motor 6| for the search signal generator 35 and associated apparatus. The resultant search signal produced during scanning cycles of preferably one minute duration vary in frequency in a stepwise fashion, each step having a frequency exactly equal to the transmitting frequency of certain chosen pass bands to which the wave signal receiver I0 is likely to be tuned. When the wave signal receiver I0 is tuned to a station having a frequency corresponding to the frequency of one of the discrete frequency steps of the search signal, the 5 kc. modulation component is detected in the wave signal receiver and a 5 kc. search tone is produced in the receiver which is converted to a signal by the receiver attachment I3 which is transmitted to the central station I5. This signal causes operation of the 5 kc. amplifier and relay unit I so as to energize the appropriate stylus 8'! in the recorder 68. It will be understood that for continuous scanning operation the manual switch 208 might be omitted and the contacts associated with the poles 288a and 2082) bridged by suitable conductor means. The continuous scanning aspect of the center frequency type of search signal device is very similar to that of the search signal device disclosed and claimed in the above mentioned co-pending Scherbatskoy application Serial No. 781,988. By employing the center frequency principle no audible heterodyne note occurs and the search signal may be generated with very simple means.

The search tone or response produced in the receiver H) by virtue of the search signal is inaudible when it its intensity is carefully adjusted to the correct value. Such precise adjustment of the intensity of the search tone without automatic volume control means therefore is very difiicult to attain. Consequently some audibility may exist which may be undesirable with the search tone continually recurring at one minute intervals. Such an audible search tone however would not be undesirable if it only occurred for a cycle or two while the tuning of the wave signal receiver I0 is changed. In accordance with the present invention a lock out device is provided whereby the search signal generator is locked out or prevented from operating once a station has been tuned in by the wave signal receiver. Such a lock out arrangement can be applied to all types of devices employing a cyclic frequency scanning device. As illustrated the manual control switch 265 is provided with a second position shown in dotted lines in Fig. 2c of the drawings which second position might be referred to as the lock out position. In this lockout position the switch poles 208a and 2081) interrupt the power supply circuits to the synchronous motor El and the search signal generator 35 respectively.

With a lock out arrangement it is desirable to deenergize the search signal generator when a response or search tone is produced in the wave signal receiver indicating that the wave signal receiver is tuned to a particular transmitting station. Since the stylus controlled relay I93 operates in response to the existence of a 5 kc. search tone this stylus control relay may be provided with a dual function of also acting as a lock out relay. Accordingly and as illustrated in the drawings the relay 193 is provided in addition to the normally open contacts I930: with two sets of normally closed contacts I932) and I93c respectively. The contacts I931) are connected voltage dropping resistor 226.

only at the instant of tuning.

tuning of the wave signal receiver in parallel with the pole 20812 of the manual control switch 208. The contacts i930 on the other hand are connected in parallel withthe pole 203a of the manual control switch 208. With this arrangement it is apparent that with the switch 208 in the lock out position energization of the relay 93 causes opening of the contacts 19th and I930 so as to deenergize the synchronous motor 6!, the search signal generator 35, and the all other stations styli 677, thereby efiectively producing a lock out operation as far as the search signal generator 35 is concerned.

It will be understood that without more the relay I93 will be deenergized as soon as the search tone stops and true lockout requires additional means for maintaining the relay I93 in an energized condition, once it has been picked up by the occurrence of a search tone in the wave signal receiver H). To this end the contacts l93a of the relay I93 also control the supply of a pow tential from the +B source to the plate circuit of the rectifier 190a. This circuit to the plate of the rectifier lSiia may be traced from the contacts l93a through the conductor 225, the pole 2080 of the manual control switch 208 and the Application of a positive potential to the plate of the valve 90a provides a positive bias which is applied to the grid of the valve lSla, consequently maintaining plate current flow and continued energization of the relay I93 to maintain contacts H31: 'in the closed position. With this arrangement a true lockout of the search signal generator 35 is provided and an audible search tone in the receiver will not be undesirable since it occurs The all other stations stylus 619 will not produce a continuous trace whenever the receiver I0 is turned on with the above described lockout arrangement as is the case when the continuous scanning connections are completed by the switch 208, but

the all other stations stylus 617' will produce a trace only when the wave signal receiver I0 is not search signal generator will remain locked out once it is locked out unless the receiver I0 is turned off each time before a new station is is;

tuned in. This is not the general practice of "users of wave signal receivers and in accordance with the present invention means for restarting the scanning cycle of the search signal generator when the tuning is changed are pro- 3.

vided. It would be possible for example to provide a time controlled switch in the energization circuit of the stylus control and lock out relay I93 to periodically interrupt this circuit,

as, for example, once every 10 minutes. Also recycling of the search signal generator following lock out might be controlled in response to any function representative of a change in the Hi. It is known, for example that a change in the tuning of a wave signal receiver causes a change in the automatic volume control voltage which appears in the circuit 29. Consequently this voltage may be employed to control a recycling device for the lock out relay at the central station i5.

The use of the automatic volume control voltage as a means for initiating recycling of the search signal generator 35 has one disadvantage in that it is not readily available at the top of the volume control in some receivers due to the interposition of the capacitor 3|, between the diode load resistor and the volume control. By virtue of the coupling capacitor 3| and the volume control resistor 32, a differentiating circuit is provided so that the potential at the terminal 32a is in effect a derivative of the automatic volume control voltage. By using the time integral of this voltage however a voltage substantially equivalent to the automatic volume control voltage is obtained. Accordingly the receiver attachment I3 is provided with an integrating device generally designated at 230, which is coupled to the top of the volume control 32 by means of a coupling capacitor 23!. This integrating device comprises a resistor 232, one terminal of which is connected to ground through a capacitor 233. The output of the integrating device 230 is therefore substantially equivalent to the automatic volume control voltage especially with reference to changes in the automatic volume control voltage.

For the purpose of causing the change in automatic volume control voltage to produce recycling of the lock out device at the central station I5, means must be provided in the receiver attachment [3 for supplying a distinctive signal to the central station in response to a change in the automatic volume control voltage. Such a change in the automatic volume control voltage will be a low frequency change and accordingly the output of the integrating device 236 is connected to the control electrode of a low frequency amplifier 236a which is illustrated as comprising one part of a twin triode 234. Plate voltage for i: the amplifier 234a is supplied from a source of +3 potential through a conductor 235 and a voltage dropping resistor 238. The amplified voltage at the output of the low frequency ampllfier 234a is supplied through a suitable coupling capacitor 231 to a polarized relay 233 comprising a movable switch arm 239 and the contacts 238a and 2381), one disposed at either side of the switch arm 239. If the AVG voltage increases one of the contacts 23811 or 2381) is engaged by the switch arm 239. If the AVG voltage decreases the other contact is engaged by the switch arm 239. Suitable spring means, not shown, normally bias the switch arm to the intermediate position shown. As illustrated, movement of the switch arm in either direction to engage one or the other of the contacts 238a or 2381) which are connected in parallel, causes operation or an oscillator 240 capable of producing a, signal differing from any other signals transmitted to the central station 15. As illustrated, the osc1llator 240, is specifically designated as an 8 kc. oscillator and comprises the triode 2341), forming a part of the twin triode 2554. Plate potential for the triode 23421 is supplied from the conductor 235. The output of the 8 kc. oscillator 240 is coupled to the house wiring circuit l4 through a conductor 242 and the conductor 32. With this arrangement it will be apparent that whenever a change in the automatic volume control voltage occurs a momentary 8 kc. signal is produced by the oscillator 240 and transmitted over the house wiring circuit M to the central station l5. As soon as the voltage of the automatic volume control circuit reaches an essentially steady state condition the relay Z38 assumes the position shown in Fig. 2a of the drawings so as effectively to stop the operation of the 8 kc. oscillator 240.

In order that the 8 kc. oscillations of the recycling control device may perform a control function at the central station I there is provided at the central station I5 an 8 kc. control channel which is substantially identical with the 5 kc. control channel described above. As illustrated this 8 kc. control channel comprises an 8 kc. band pass filter 2A5 and an 8 kc. amplifier and relay unit 249, very similar to the corresponding units I84 and E85 respectively. As illustrated, the 8 kc. band pass filter 245 is coupled through a suitable coupling capacitor 241 with the conductor it! which is connected to the ungrounded side of the house wiring circuit I4 through the contacts $3M of the relay I31. The output of the band pass filter 245 is coupled to the 8 kc. amplifier and relay unit 246 through a suitable coupling capacitor 248.

In order that the 8 kc. signal passed by the band pass filter 2'35 may initiate recycling of the search signal generator 35, it is preferably supplied in succession to an 8 kc. amplifier I891), a rectifier I991) and a direct current amplifier I9Ib which direct current amplifier i adapted to control the energization of the winding 202' of the recycling control relay 282. The amplifiers I892) and I9) and the rectifier I961; are illustrated as forming a part of the twin tubes I89, [SI and I99 respectively, the other sections of which are employed as described above in the 5 kc. amplifier and relay unit I85. The output of the 8 kc. band pass filter 2 55 is connected to the control electrode of the amplifier I891). The plate circuit of the amplifier [89b is coupled to the rectifier I9Ilb through a suitable coupling capacitor 249. The cathode of the rectifier I991) is connected through a resistor 250 with the control electrode of the direct current amplifier ISIb. In order to prevent operation of the 8 kc. amplifier and relay unit 245 unless an 8 kc. signal produced by the oscillator 240 is received a negative bias potential from the voltage divider IE3 is supplied to the control electrode of the direct current amplifier I9Ib through a resistor ESL and to the plate of the rectifier I98!) through a resistor 252. A suitable capacitor 253 connected across the resistor I cooperates with the resistor 25!! so as to provide a circuit with a long time constant to prevent any signal such as static or an occasional click from causing inadvertent operation of the 8 kc. amplifier and relay unit 246.

Plate potential is supplied to the amplifier I89b from the conductor I62 which is a source of +13 potential through a resistor 255. The plate circuit of the direct current amplifier Hill) on the other hand is connected to the conductor I62 which is a source of +3 potential through the winding 202 of the relay 202 and the milliammeter 258. The magnitude of the bias potential applied from the unit I83 to the control electrode of the direct current amplifier I9 Ib is adjusted so that a low current for example of one milliampere flows through the milliammeter 256 and the winding 2E2 when no 8 kc. signal is received, which current is insufficient to cause operation of the relay 292. Upon the receipt of an 8 kc. signal, however, the direct current amplifier I9 I1) is rendered much more conductive and a sufiiciently higher current flows through the winding 202' causing the relay 282 to open its normally closed contacts 262a. Since the contacts 202a control the supply of +3 potential to the winding I33 of the stylus control and lock out relay I93, energization of the recycling relay 202 causes deenergization of the lock out and stylus control relay I93. With this arrangement it is apparent that recycling of the search signal generator 35 through deenergization of the relay I93 is caused whenever the tuning of the wave signal receiver I0 is changed.

It will be apparent that any type of system employing a lock out arrangement responsive to the receipt of a particular type of signal can lock out in response to an incorrect signal. For the purpose of minimizing the possibility of locking out the search signal generator 35 in response to an incorrect signal the recycling control channel is in accordance with the present invention made more sensitive than the 5 kc. channel in the central station I5. This is true of the arrangement described above by virtue of the built in attenuator comprising the resistor I88 in the 5 kc. band pass filter I84, which is not present in the 8 kc. band pass filter 245. Consequently a sudden burst of static or a sudden very intense noise on the house wiring circuit I4 cannot cause incorrect logging of the tuning condition of the wave signal receiver I0 since it will also cause recycling. Consequently anything which causes false log ging also causes immediate recycling.

If the search tone in the wave signal receiver should be too strong, as, for example, during daytime reception of a distant station which is normally received at night, such a strong search tone could cause slight operation of the automatic volume control circuit in the wave signal receiver III, with the resultant recycling of the search Signal generator 35. To avoid such undesirable recycling at the instant of logging the tuning condition of the wave signal receiver I0, means are provided to desensitize the recycling circuit at the instant of the production of the search tone. This is accomplished as illustrated in the drawings by employing the surge voltage produced in the plate circuit of the direct current amplifier i9|a in response to the sudden increase in current causing energization of the relay I93 to desensitize the 8 kc. amplifier I891). To this end the plate circuit of the direct current amplifier ISM. is paralleled with a circuit comprising the capacitor 260 and the resistor 26 I. The nega tive pulse of voltage produced across the condenser 260 upon energization of the relay I93 appears at the ungrounded terminal of the resistor ZGI designated at 262 and is supplied to the control electrode of the 8 kc. amplifier I89b through a voltage dropping resistor 263. It will be apparent that a voltage impulse will also be produced when the relay I93 is deenergized, but since the impulse is in the reverse direction it will not desensitize the recycling control circuit. In order to remove the charge on the condenser 260 so as not to desensitize the control circuit at any t me except when a response occurs in the wave signal receiver I0 the contacts 20% of the recycling control relay 202 are adapted momentarily to connect the condenser 269 across the inductance of the winding I93 whenever the recycling control relay 232 is energized. It will be apparent that the arrangement for desensitizing the recycling control channel at the instant of logging and making the recycling control channel norngefillty more sensitive than the 5 kc. channel is a s e y provision to reve the system. D nt incorrect operation of If the receiver attachment is not conn the receiver II], but a microphone is empl yfizg a: 1n the above mentioned Scherbatskoy co-pendin application, then it would also b undesirabl to make a connection with the receiver II] for obtam ng a potential representative of the automatic volume control voltage. Under these conditions the low frequency amplifier 34a might be 25 energized in response to a signal produced when the tuning of the wave signal receiver I is changed. For example, the tuning control or the push buttons of a receiver might be provided with a permanent magnet movable therewith. Associated with the permanent magnet could be a small stationary coil connected to the control electrode of the low frequency amplifier 23cc. Movement of the tuning control and consequently of the permanent magnet would induce a current in the adjacent stationary coil to initiate the recycling device in the receiver attachment l3 and consequently cause an 8 kc. oscillation to be produced by the oscillator 24:].

In View of the detailed description included above the operation of the lock out device and automatic recycling control described above will be apparent and no further discussion thereof is included herein. Due to the lock out control and recycling feature of the present invention it is not essential that the search tone be inaudible since it occurs only at the instant of tuning a receiver to a station and then does not again occur until a new station is tuned in.

In the arrangement described above the lock out arrangement silences the search signal generator on all channels once a response is received on any channel. In Figs. la and ab of the drawings there is disclosed an arrangement in which look out occurs on the channel tuned in by the wave signal receiver and the search signal is sent out on all other channels. Whenever one of the other channels shows a response, release of lock out is obtained. The corresponding parts of Figs. 4c and 4b of the drawings are designated by the same reference numerals as in the preceding figures.

Since the lock out is released in response to the production of a response in another channel, it is unnecessary to rely on a change in the AVG voltage of the receiver and the receiver attachment I3 is considerably simplified over that shown in Fig. 2a of the drawings since the integrating device 230, the amplifier 234a, the relay 238 and the B kc. oscillator 24?! are not required.

The search signal generator ,35 on the other hand is substantially identical with the search signal generator 35 shown in Fig. 2b of the drawings and certain portions thereof have been omitted to simplify the drawings. As in Fig. 2b of the drawings the synchronous motor 5| drives at one revolution per minute the rotating switch arms 45 and 56. However, the rotating switch 64 is no longer driven by the synchronous motor 6!, but instead is driven by an independent synchronous motor 366 which is also capable of rotating its shaft 366 at one revolution per minute. The synchronous motor t! on the other hand has its shaft 6| connected to rotate a rotatable switch arm 3M which is adapted to successively engage cooperating contacts 382a, 302b, 362e, 302d, 302e, 302i, 302g, 36272 3322' and 3M9, which are arranged on the circumference of a circle in exactly the same manner as the contacts 45 with the contacts marked with the same subscript, being positioned so as to be simultaneously engaged by their respective switch arms 45 and 3ill. The switch arm 3M has been illustrated as of a somewhat difierent type than the switch arms 45 and 56 and it may be designated as of the so-oalled shorting type, i. e. the arm Sill makes contact momentarily with two adjacent contacts when passing from one to the other whereas the switch arms 45 and 56 are adapted to engage only a single contact at a time.

, as to control a suitable means for locking out a particular channel to which the wave signal receiver I0 is tuned.

For the purpose of relating the synchronous motor 5| to the synchronous motor 390 there is provided a rotating switch mechanism comprising a rotating switch arm S65 and associated contacts 3360a, 5366b, 3060, 366d, 306e, 306i, 3069, 313th, 3%81, and 3657' which are arranged in equal- 1y spaced relationship on the circumference of a circle in the same manner as the contacts 392. The rotary switch arm is further connected to the shaft 306' so as to be rotated in a counterclockwise direction as viewed in Fig. 4a of the drawings upon operation of the synchronous motor 300. The contacts 356 are arranged so that those contacts marked with corresponding subscripts are in identical positions with the corresponding contacts 332. Furthermore the contacts with corresponding subscripts are interconnected by suitable conductors as is clearly shown in Fig. 4a of the drawings. The rotatable switch arm 39! is connected to ground as illustrated while the rotatable switch arm 365 is connected by means of a conductor 3!}? through the winding 303 of a relay 308 to a source of +B potential indicated as the conductor 2| I. With this arrangement it is apparent that the relay ass is energized whenever the switch arms 39! and 3&5 are disposed on their associated contacts marked with the same subscript. The switch arm 305 is furthermore illustrated as of the shorting type similar to the switch arm 30 I.

In order to perform suitable control operations the relay 308 is provided with two sets of F normally open contacts 398a and 30th and two sets of normally closed contacts 3080 and 308d. The normally open contacts 398a control the energizing circuit for the synchronous motor 35!] which has one terminal thereof connected through the conductor 3!!! and the contacts 308a to the conductor 63 of the synchronous motor 6| which as was mentioned above is connected to the power supply unit IZI. The other terminal of the synchronous motor 305 is directly connected to the conductor 62 which as was described above is also connected to the other terminal of the synchronous motor 61. It will be apparent that the synchronous motor 360 is energized whenever the relay 388 is actuated to close its contacts 308a. When, however, the relay 368 is in the position shown in Fig. 4b of the drawings the synchronous motor 309 is deenergized.

In order that the synchronous motor 360 may look out only a single channel of the search signal generator 35 there is provided an additional rotating switch mechanism comprising the rotating arm 3l2 which is drivingly connected to the shaft 300'. The switch arm 312 is adapted to successively engage the contacts MM, 3131), M30, 3i3d, 343e, M3 M39, tiSh, 353i, and slay inclusive which are arranged in spaced relationship about the circumference of a circle in exactly the same manner as the contacts 44 so that those contacts with corresponding subscripts occupy identical positions with reference to their associated circular arrangement. As illustrated the rotating switch arm 312 is grounded through a conductor 314 and the normally closed contacts 368d of the relay 308. The contacts 3i3a to 3137 inclusive are connected through a suitable cable 3H to the contacts 44a, to 441 respectively. With this arrangement it is apparent that whatever contact is engaged by the rotating switch arm 3| 2 the corresponding contact 44 is grounded when the contacts 308d of the relay 308 is closed, which effectively means that the control electrode 48 of the portion 35a of the search signal generator 35 is rendered ineffective to produce a search signal on a particular 1:

channel corresponding to the contact 3l3 engaged by the switch arm 3I2. The contacts 313g, 3fl3h, and 3l3i are connected by suitable conductors 3l5 g, 3l5h, and 3l5i' respectively with the terminals 519, 81h and 871 of the control elec-, trodes 8? of the very high frequency oscillators l ll. With this arrangement the particular oscillator corresponding to the contact 3l 3g, 31311, or 313i engaged by the switch arm 3|2 is rendered ineffective to produce a search signal when the relay 3% is deenergized.

The rotary switch mechanism comprising the rotating switch arm es and the contacts 85 forming a portion of the recorder 68 is identical in Fig. 4a with the recorder 68 of Fig. 212. However,

the rotating switch arm 64 is drivingly connected to theshaf t ase' rather than the shaft 6!.

In view of the fact that the central station I5 of Figs. 4c and 4b need not receive an 8 kc. signal as was the case in Fig. 2c, the twin triode amplifier I89 is dispensed with and instead the output of the 5 kcl bandpass filter IE4 is connected to the control electrode of a triode I891. The twin diode I50 and the twin triode |9| are retained however to provide two separate chan nels for passing responses occurring by virtue of the. wave signal receiver It] being tuned to different channels. The corresponding parts are identical in general with those shown in the pre: ceding figures and are designated by the same reference numerals Th relay H93 differs only in that one set of contacts [Q30 has been omitted. Similarly the relay having the winding differ s from that shown in Fig. 2c in that the set of contacts ZiiZb has been omitted. Also the resisto'r i95 the capacitor I89 and the resistor I91 are designed to have a much longer time constant than in the preceding figures, whereupon the contact arm 30! is capable of moving from one contact to another inthe time it takes to build u a positive bias on the resistor I91. It will be understood that the resistors m5 and an and the capacitor I59 as well as the resistors 0 and 251 and the capacitor 253 provide time constant or integrating circuits which prevent noise or surge s from being transmitted.

' In accordance with the present invention the coupling capacitor I94 is adapted alternately to connect the output of the amplifier l89a with either the rectifier 191111 or the rectifier I902) through contacts filial? or 308a respectively. Consequently depending upon the position of the reat, s the channel comprising the rectifier l9 0a and the direct current amplifier l9 la or the channel comprising the rectifier lane and the direct current amplifier l9|b are rendered effective, the first mentioned channel being connected to. the winding [93" of the relay [9.3 while. the second mentioned channel is connected to the. winding 202" of the corresponding relay 202.

For the purpose of maintaining the relay I93 energized once a search tone or response has been produced the contacts 33a thereof as in the preceding figures are adapted to control the supply of +B potential from the conductor Hi2 through a voltage dropping resistor 320 to the plate circuit of the rectifier a. Preferably the relay N13 is designed so that the current flow for causing operation thereof to close contacts E93Ct is three or four times greater than the value necessary to hold these contacts in the closed position. The potential applied through voltage dropping resistor 320 is only sufiicient to hold the relay I93 in its closed position with reference to contacts 193a, and is substantially below the current pick up value thereof.

Assume for example that the central station I5 is deenergized and the synchronous motors iii and 300 with their associated rotary switch mechanisms are in the positions shown. Upon tuning the Wave signal receiver 10 to a particular Chan nel the power supply unit I20 of the central station 15' is energized with the result that the synchronous motor 5! begins to rotate the switch arms 45, 55 and 361 i in the direction of the arrows of Fig. 40, at one revolution per minute. Since the contacts 308a are open the synchronous n otor 300 is not energized. A search signal is produced at this time by the search signal generator 35 on all channels except the one rendered ineffective by the particular position of the switch arm 3|2. As soon as the rotating switch arm 3M has rotated so as to assume the same position as that of the rotating switch arm 305 a circuit is completed through the relay winding 308 thereby closing the contacts 308d and energizing the synchronous motor 300 which continues to rotate in synchronism with the syn: chronous motor 6|. The rotating switch mechanism comprising the rotating arm 64, operates in exactly the same manner as in the preceding figures with reference to the all other stations stylus 617' and the like. The synchronous motors BI and 300 continue to rotate in synchronism as long as the relays [93 and 202 remain in the position shown in the Fig. 4b,. Also when relay 308 is energized the search signal is effective on all channels represented. Upon the occurrence of a search tone a response is produced which is received at the central station l5. Since the relay 308 is energized the contacts 3081). are closed and the contacts 308a are open. The response therefore is transmitted to the channel comprising the rectifier [911a so as to energize the relay [33 which closes its contacts 193a and opens its contacts I931), Opening of the contacts l9 3b immediately deenergizes the relay 308 so. as to open its contacts 3080; to deenergize the synchronous motor 300.. At this time the contact arm 3| 2 will ground the particular channel of the search signal generator 35 corresponding to the channel to which the wave signal receiver I0 is tuned through the conductor 3 l4 and the contacts 308d of the relay 308. The search signal generator will therefore continue to produce a search signal on all channels except the particular one to which the wave signal receiver is, tuned and effectively therefore the single channel to which the receiver 10 is tuned is locked out and all the other channels are effective as far as the search signal is concerned.

It will be understood that the deenergi-zation of the relay 308 will also cause contacts 31180 to close so as to connect the channel comprising the rectifier [9% with the output of the amplifier 

